Coolant transfer system and method for a dual-wall airfoil

ABSTRACT

A dual-wall airfoil configured for coolant transfer includes a spar having a pressure side wall and a suction side wall each including raised features on an outer surface thereof. An interior of the spar includes coolant cavities. An inner surface of a pressure side coversheet is in contact with the raised features on the outer surface of the pressure side wall so as to define pressure side flow pathways between the pressure side wall and the pressure side coversheet, and an inner surface of a suction side coversheet is in contact with the raised features on the outer surface of the suction side wall so as to define suction side flow pathways between the suction side wall and the suction side coversheet. The pressure side flow pathways and/or the suction side flow pathways include cooling circuit(s) configured to transfer coolant between the coolant cavities.

TECHNICAL FIELD

This disclosure relates generally to airfoils with dual-wall cooling andmore particularly to a coolant transfer system and method for adual-wall airfoil.

BACKGROUND

Gas turbine engines include a compressor, combustor and turbine in flowseries along a common shaft. Compressed air from the compressor is mixedwith fuel in the combustor to generate hot combustion gases that rotatethe turbine blades and drive the compressor. Improvements in the thrustand efficiency of gas turbine engines are linked to increasing turbineentry temperatures, which places a heavy burden on turbine blades.Consequently, there is significant interest in developing improvedcooling techniques for airfoils in gas turbine engines. Dual-wall ordouble-wall cooling configurations are promising advancements for thecooling of turbine blades and nozzle guide vanes.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments may be better understood with reference to the followingdrawings and description. The components in the figures are notnecessarily to scale. Moreover, in the figures, like-referenced numeralsdesignate corresponding parts throughout the different views.

FIG. 1A is an exploded assembly view of the pressure side of anexemplary airfoil with dual-wall cooling and a pressure side coolingcircuit configured for transfer of coolant between coolant cavities.

FIG. 1B is an exploded assembly view of the suction side of an exemplaryairfoil with dual-wall cooling and a suction side cooling circuitconfigured for transfer of coolant between coolant cavities.

FIG. 2 is a cross-sectional view of the dual-wall airfoil of FIGS. 1Aand 1B, with arrows to show flow pathways for coolant.

FIG. 3 is a cross-sectional view of an exemplary gas turbine engine thatmay include the airfoil described in this disclosure.

DETAILED DESCRIPTION

A dual-wall or double-wall airfoil for a gas turbine engine may includea hollow spar that is partially or completely surrounded by suction sideand pressure side coversheets (or “skins”) and spaced apart from thecoversheets by raised features on the outer surface of the spar. Theseraised features may include pedestals and/or rails arranged to defineflow pathways for coolant (e.g., air) between the outer surface of thespar and the respective coversheet. The coolant may provide heattransfer and cooling as it traverses the flow pathways before exiting,typically through exit holes in the respective coversheet or throughexit slots. The coolant is delivered into the flow pathways from coolantcavities in the spar that are fed through inlets at the base of thespar. In some situations, one of the inlets, typically the inlet thatfeeds into the coolant cavity nearest to the trailing edge, may bepartially or completely blocked by other component(s), such that coolantflow into that particular coolant cavity is inhibited or prevented. Inthis disclosure, selected flow pathways between the outer surface of thespar and the coversheets are configured to transfer coolant from onecoolant cavity to another, thereby ensuring that each coolant cavity isequipped to supply the coolant needed to different parts of the airfoil.

FIGS. 1A and 1B show pressure and suction sides, respectively, of anairfoil with dual-wall cooling that includes one or more coolingcircuits for transfer of coolant between coolant cavities. The dual-wallairfoil 100 (which may alternately be referred to as “the airfoil 100”)comprises a spar 102 having a pressure side wall 104 and a suction sidewall 106 meeting at a leading edge 108 and a trailing edge 110 of theairfoil 100. Each of the pressure side wall 104 and the suction sidewall 106 includes raised features 118 on an outer surface 104 a, 106 athereof. A pressure side coversheet 114 overlies the pressure side wall104, and an inner surface 114 a of the pressure side coversheet 114 isin contact with (e.g., bonded to or integrally formed with) the raisedfeatures 118 on the outer surface 104 a of the pressure side wall 104,thereby defining pressure side flow pathways 124 between the pressureside wall 104 and the pressure side coversheet 114. A suction sidecoversheet 116 overlies the suction side wall 106, and an inner surface116 a of the suction side coversheet 116 is in contact with (e.g.,bonded to or integrally formed with) the raised features 118 on theouter surface 106 a of the suction side wall 106, thereby definingsuction side flow pathways 126 between the suction side wall 106 and thesuction side coversheet 116. An interior of the spar 102 includescoolant cavities 112 for providing coolant to the pressure side andsuction side flow pathways 124,126 through inlet holes in the pressureand suction side walls 104,106. For example, as shown in FIGS. 1A and1B, the interior of the spar 102 may include three coolant cavities 112a,112 b,112 c separated by ribs 148 that extend across the interior fromthe pressure side wall 104 to the suction side wall 106. Alternatively,the interior of the spar 102 may include another number of coolantcavities 112, such as two, four, or five coolant cavities 112.

The raised features 118 may have a height that corresponds to thespacing between the outer surface 104 a,106 a of the side wall 104,106and the respective coversheet 114,116. Typically, the raised features118 take the form of pedestals or rails. However, the raised features118 shown on the pressure and suction sides of the airfoil 100 in FIGS.1A and 1B are merely exemplary and may alternatively have differentshapes, sizes, orientations and/or arrangements than those shown here,so long as pressure side and suction side flow pathways 124,126 aredefined.

Referring to FIG. 2 , the pressure side flow pathways 124 may include apressure side cooling circuit 120 configured to direct coolant from oneof the coolant cavities 112 (such as a first or second of the coolantcavities 112) into another of the coolant cavities 112. Also oralternatively, the suction side flow pathways 126 may include a suctionside cooling circuit 122 configured to direct coolant from the first orsecond of the coolant cavities 112 into the other of the coolantcavities 112. It is noted that the term “first or second of the coolantcavities” 112 may refer to any of the coolant cavities 112 in theinterior of the spar 102; for example, the term may be replaced with“leading edge or midspan coolant cavity 112 a,112 b,” “leading edge ortrailing edge coolant cavity 112 a,112 c,” or with “midspan or trailingedge coolant cavity 112 b,112 c.” Similarly, the term “another of thecoolant cavities” or “the other of the coolant cavities” may refer tothe leading edge, midspan or trailing edge coolant cavity 112 a,112b,112 c. Since, as indicated above, the interior of the spar 102 mayinclude more than three coolant cavities 112, it is recognized thatthere may be more than one midspan coolant cavity 112 b. As shown by thearrows in FIG. 2 , coolant in the suction side cooling circuit 122and/or the pressure side cooling circuit 120 may travel toward thetrailing edge 110 of the airfoil 100 before being directed into theother of the coolant cavities 112. Also or alternatively, coolant in thesuction side cooling circuit 122 and/or the pressure side coolingcircuit 120 may travel toward the leading edge 108 of the airfoil 100before being directed into the other of the coolant cavities 112. Asillustrated in FIGS. 1A and 1B, the pressure (or suction) side coolingcircuit 120,122 includes a portion of the raised features 118 on thepressure (or suction) side wall 104,106.

Referring to the example of FIG. 2 , the pressure side cooling circuit120 is in fluid communication with the first or second of the coolantcavities 112, which may be a leading edge coolant cavity 112 a (asillustrated) or a midspan coolant cavity 112 b, via inlet holes 128 inthe pressure side wall 104, and in fluid communication with the other ofthe coolant cavities 112, which may be a trailing edge coolant cavity112 c, via outlet holes 130 in the pressure side wall 104. The terms“inlet” and “outlet” are used to indicate the direction of coolant flowwith respect to the pressure side cooling circuit 120, that is, whetherthe coolant is moving into or out of the cooling circuit 120.Accordingly, the outlet holes 130 are positioned downstream of the inletholes 128. Also or alternatively, the outlet holes 130 may be positionedcloser to the trailing edge than the inlet holes 128.

Similarly, the suction side cooling circuit 122 of this example is influid communication with the first or second of the coolant cavities112, which may be the midspan coolant cavity 112 b (as shown) or theleading edge coolant cavity 112 a, via inlet holes 132 in the suctionside wall 106, and in fluid communication with the other of the coolantcavities 112, which may be the trailing edge coolant cavity 112 c, viaoutlet holes 134 in the suction side wall 106. As above, the terms“inlet” and “outlet” are used to indicate the direction of coolant flowwith respect to the cooling circuit 122, that is, whether the coolant ismoving into or out of the cooling circuit 122, respectively.Accordingly, the outlet holes 134 are positioned downstream of the inletholes 132. Also or alternatively, the outlet holes 134 may be positionedcloser to the trailing edge than the inlet holes 132.

Other pressure side and/or suction side cooling circuits 140 may beconfigured to direct coolant from one of the coolant cavities 112,through the respective cooling circuit to effect heat transfer, and thenout of the airfoil 100 (instead of between coolant cavities 112). Suchcooling circuits 140 are fed by different inlet holes than the pressureside and suction side cooling circuits 120,122 described above. Thecoolant in the other cooling circuits 140 may flow in any desireddirection (e.g., toward the leading edge 108 or toward the trailing edge110) before exiting the airfoil 100 (e.g., through exit holes 142 in thepressure and/or suction side coversheets 114,116).

For example, referring to FIG. 1A and FIG. 2 , there may be a PStrailing edge cooling circuit 144 between the pressure side coolingcircuit 120 and the trailing edge 110 of the airfoil. The PS trailingedge cooling circuit 144 may be fed by coolant from the trailing edgecoolant cavity 112 c via additional inlet holes 138 in the pressure sidewall 104. Without the pressure side cooling circuit 120 to transfercoolant from the leading edge or midspan coolant cavity 112 a,112 b tothe trailing edge coolant cavity 112 c, it might not be possible toprovide sufficient coolant to the PS trailing edge cooling circuit 144.Also, as shown in FIG. 1B and FIG. 2 , there may be a SS trailing edgecooling circuit 146 between the suction side cooling circuit 122 and thetrailing edge 110 of the airfoil. The SS trailing edge cooling circuit146 may be fed by coolant from the trailing edge coolant cavity 112 cvia additional additional inlet holes 136 in the suction side wall 106.Without the suction side cooling circuit 122 to transfer coolant fromthe leading edge or midspan coolant cavity 112 a,112 b to the trailingedge coolant cavity 112 c, it might not be possible to providesufficient coolant to the SS trailing edge cooling circuit 146.

Also described in this disclosure is a method of cooling an airfoil thatincludes providing (as shown in FIGS. 1A and 1B and described above): aspar 102 having a pressure side wall 104 and a suction side wall 106meeting at a leading edge 108 and a trailing edge 110 of the airfoil100, where each of the pressure side wall 104 and the suction side wall106 includes raised features 118 on an outer surface 104 a,106 athereof; a pressure side coversheet 114 overlying the pressure side wall104, where an inner surface of the pressure side coversheet 114 is incontact with (e.g., bonded to or integrally formed with) the raisedfeatures 118 on the outer surface 104 a of the pressure side wall 104,thereby defining pressure side flow pathways 124 between the pressureside wall 104 and the pressure side coversheet 114; and a suction sidecoversheet 116 overlying the suction side wall 106, where an innersurface 116 a of the suction side coversheet 116 is in contact with(e.g., bonded to or integrally formed with) the raised features 118 onthe outer surface 106 a of the suction side wall 106, thereby definingsuction side flow pathways 126 between the suction side wall 106 and thesuction side coversheet 116. An interior of the spar 102 includescoolant cavities 112 for providing coolant to the pressure side andsuction side flow pathways 124,126, which may include a pressure sidecooling circuit 120 and/or a suction side cooling circuit 122. Themethod further includes delivering coolant from a first and/or a secondof the coolant cavities 112 into another of the coolant cavities 112through the pressure side and/or the suction side cooling circuit120,122. As above, it is noted that the term “first and/or a second ofthe coolant cavities” 112 may refer to any of the coolant cavities 112in the interior of the spar 102; for example, the term may be replacedwith “leading edge coolant cavity 112 a and/or midspan coolant cavity112 b,” “leading edge coolant cavity 112 a and/or trailing edge coolantcavity 112 c,” or with “midspan coolant cavity 112 b and/or trailingedge coolant cavity 112 c.” Similarly, the term “another of the coolantcavities” or “the other of the coolant cavities” may refer to theleading edge, midspan or trailing edge coolant cavity 112 a,112 b,112 c.Since, as indicated above, the interior of the spar 102 may include morethan three coolant cavities 112, it is recognized that there may be morethan one midspan coolant cavity 112 b.

In one example, the coolant may be delivered from the leading edgecoolant cavity 112 a and/or the midspan coolant cavity 112 b into thetrailing edge coolant cavity 112 c via the pressure side and/or suctionside cooling circuits 120,122. Accordingly, delivering the coolantthrough the pressure side cooling circuit 120 and/or the suction sidecooling circuit 122 may comprise directing the coolant toward thetrailing edge 110 of the airfoil 100. In another example, the coolantmay be delivered from the trailing edge coolant cavity 112 c and/or themidspan coolant cavity 112 b into the leading edge coolant cavity 112 avia the pressure side and/or the suction side cooling circuits 120,122.Accordingly, delivering the coolant through the pressure side coolingcircuit 120 and/or the suction side cooling circuit 122 may comprisedirecting the coolant toward the leading edge 108 of the airfoil 100.

As described above, the pressure side cooling circuit 120 may be influid communication with the first or second of the coolant cavities112, which may be the leading edge coolant cavity 112 a or the midspancoolant cavity 112 b, via inlet holes 128 in the pressure side wall 104,and in fluid communication with the other of the coolant cavities 112,which may be the trailing edge coolant cavity 112 c, via outlet holes130 in the pressure side wall 104. Similarly, the suction side coolingcircuit 122 may be in fluid communication with the first or second ofthe coolant cavities 112, which may be the midspan coolant cavity 112 bor the leading edge coolant cavity 112 a, via inlet holes 132 in thesuction side wall 106, and in fluid communication with the other of thecoolant cavities 112, which may be the trailing edge coolant cavity 112c, via outlet holes 134 in the suction side wall 106.

The pressure side and suction side cooling circuits 120,122 may work intandem; for example, the coolant may be delivered from the leading edgecoolant cavity 112 a into the trailing edge coolant cavity 112 c throughthe pressure side cooling circuit 120, while the coolant is deliveredfrom the midspan coolant cavity 112 b into the trailing edge coolantcavity 112 c through the suction side cooling circuit 122, asillustrated in FIG. 2 . Alternatively, the coolant may be delivered fromthe midspan coolant cavity 112 b into the trailing edge coolant cavity112 c through the pressure side cooling circuit 120, while the coolantis delivered from the leading edge coolant cavity 112 a into thetrailing edge coolant cavity 112 c through the suction side coolingcircuit 122.

Also, as described above, the pressure side wall 104 may includeadditional inlet holes 138 in fluid communication with the trailing edgecoolant cavity 112 c, and the method may further comprise delivering thecoolant from the trailing edge coolant cavity 112 c into a PS trailingedge cooling circuit 144. Also or alternatively, the suction side wall106 may include additional inlet holes 136 in fluid communication withthe trailing edge coolant cavity 112 c, and the method may furthercomprise delivering the coolant from the trailing edge coolant cavity112 c into a SS trailing edge cooling circuit 146. Delivery of thecoolant from the trailing edge coolant cavity 112 c into the trailingedge cooling circuit(s) 144,146 may occur only after the coolant hasbeen delivered from the leading edge coolant cavity 112 a and/or themidspan coolant cavity 112 b.

The dual-wall airfoil 100 described herein may be fabricated usinginvestment casting and diffusion bonding methods known in the art, suchas described in U.S. Pat. No. 6,003,754, entitled “Airfoil for a GasTurbine Engine and Method of Manufacture,” which is hereby incorporatedby reference in its entirety. The airfoil 100, including the spar 102and the pressure and suction side coversheets 114,116, may be formedfrom one or more materials that have high melting points, goodoxidation/corrosion resistance and high-temperature strength. Forexample, a nickel-base alloy, a titanium-base alloy, and/or an iron-basealloy may be suitable. The alloy may have an equiaxed, directionallysolidified, or single-crystal microstructure. The raised features 118may be integrally formed with the airfoil 100, or, more specifically,may be integrally formed on the respective suction or pressure side wall106,104. The raised features 118 may be bonded to or integrally formedwith the respective suction or pressure side coversheet 120,140. Theairfoil 100 may have a single-piece or a multi-piece construction.

A gas turbine engine 300, such as that shown in FIG. 3 , may include theairfoil 100 described above, e.g., as a nozzle guide vane or a turbineblade 312 in the turbine section 310. In some examples, the gas turbineengine 300 may supply power to and/or provide propulsion of an aircraft,e.g., a helicopter, an airplane, an unmanned space vehicle, a fixed wingvehicle, a variable wing vehicle, a rotary wing vehicle, an unmannedcombat aerial vehicle, a tailless aircraft, a hover craft, and/or anextraterrestrial (spacecraft) vehicle. Also or alternatively, the gasturbine engine 300 may be utilized in a configuration unrelated to anaircraft such as, for example, an industrial application, an energyapplication, a power plant, a pumping set, a marine application (forexample, for naval propulsion), a weapon system, a security system, aperimeter defense or security system.

To clarify the use of and to hereby provide notice to the public, thephrases “at least one of <A>, <B>, . . . and <N>” or “at least one of<A>, <B>, . . . or <N>” or “at least one of <A>, <B>, . . . <N>, orcombinations thereof” or “<A>, <B>, . . . and/or <N>” are defined by theApplicant in the broadest sense, superseding any other implieddefinitions hereinbefore or hereinafter unless expressly asserted by theApplicant to the contrary, to mean one or more elements selected fromthe group comprising A, B, . . . and N. In other words, the phrases meanany combination of one or more of the elements A, B, . . . or Nincluding any one element alone or the one element in combination withone or more of the other elements which may also include, incombination, additional elements not listed. Unless otherwise indicatedor the context suggests otherwise, as used herein, “a” or “an” means “atleast one” or “one or more.”

While various embodiments have been described, it will be apparent tothose of ordinary skill in the art that many more embodiments andimplementations are possible. Accordingly, the embodiments describedherein are examples, not the only possible embodiments andimplementations.

The subject-matter of the disclosure may also relate, among others, tothe following aspects:

A first aspect relates to a dual-wall airfoil configured for coolanttransfer, the airfoil comprising: a spar having a pressure side wall anda suction side wall meeting at a leading edge and a trailing edge of theairfoil, each of the pressure side wall and the suction side wallincluding raised features on an outer surface thereof, an interior ofthe spar including coolant cavities; a pressure side coversheetoverlying the pressure side wall, an inner surface of the pressure sidecoversheet being in contact with the raised features on the outersurface of the pressure side wall, thereby defining pressure side flowpathways between the pressure side wall and the pressure sidecoversheet; a suction side coversheet overlying the suction side wall,an inner surface of the suction side coversheet being in contact withthe raised features on the outer surface of the suction side wall,thereby defining suction side flow pathways between the suction sidewall and the suction side coversheet; wherein the pressure side flowpathways include a pressure side cooling circuit configured to directcoolant from a first or second of the coolant cavities into another ofthe coolant cavities, and/or wherein the suction side flow pathwaysinclude a suction side cooling circuit configured to direct coolant fromthe first or second of the coolant cavities into the other of thecoolant cavities.

A second aspect relates to the airfoil of the first aspect, wherein thepressure side cooling circuit is in fluid communication with the firstor second of the coolant cavities via inlet holes in the pressure sidewall, and in fluid communication with the other of the coolant cavitiesvia outlet holes in the pressure side wall.

A third aspect relates to the airfoil of the first or second aspect,wherein the suction side cooling circuit is in fluid communication withthe first or second of the coolant cavities via inlet holes in thesuction side wall, and in fluid communication with the other of thecoolant cavities via outlet holes in the suction side wall.

A fourth aspect relates to the airfoil of any preceding aspect, whereinthe coolant in the suction side cooling circuit and/or the pressure sidecooling circuit travels toward the leading edge of the airfoil beforebeing directed into the other of the coolant cavities.

A fifth aspect relates to the airfoil of any preceding aspect, whereinthe first or second of the coolant cavities comprises a trailing edgecoolant cavity or a midspan coolant cavity, and wherein the other of thecoolant cavities is a leading edge coolant cavity.

A sixth aspect relates to the airfoil of any preceding aspect, whereinthe coolant in the suction side cooling circuit and/or the pressure sidecooling circuit travels toward the trailing edge of the airfoil beforebeing directed into the other of the coolant cavities.

A seventh aspect relates to the airfoil of any preceding aspect, whereinthe first or second of the coolant cavities comprises a leading edgecoolant cavity or a midspan coolant cavity, and wherein the other of thecoolant cavities is a trailing edge coolant cavity.

An eighth aspect relates to the airfoil of the seventh aspect, whereinthe pressure side cooling circuit is in fluid communication with theleading edge coolant cavity via inlet holes in the pressure side wall,and in fluid communication with the trailing edge coolant cavity viaoutlet holes in the pressure side wall.

A ninth aspect relates to the airfoil of the eighth aspect, wherein thepressure side wall includes additional inlet holes in fluidcommunication with the trailing edge coolant cavity for delivering thecoolant from the trailing edge coolant cavity into a PS trailing edgecooling circuit.

A tenth aspect relates to the airfoil of the seventh aspect, wherein thesuction side cooling circuit is in fluid communication with the midspancoolant cavity via the inlet holes in the suction side wall, and influid communication with the trailing edge coolant cavity via the outletholes in the suction side wall.

An eleventh aspect relates to the airfoil of the tenth aspect, whereinthe suction side wall includes additional inlet holes in fluidcommunication with the trailing edge coolant cavity for delivering thecoolant from the trailing edge coolant cavity into a SS trailing edgecooling circuit.

A twelfth aspect relates to the airfoil of any preceding aspect, whereinthe suction side cooling circuit includes at least a portion of theraised features on the suction side wall, and/or wherein the pressureside cooling circuit includes at least a portion of the raised featureson the pressure side wall.

A thirteenth aspect relates to a gas turbine engine including theairfoil of any preceding aspect.

A fourteenth aspect relates to a method of transferring coolant in adual-wall airfoil, the method comprising providing an airfoilcomprising: a spar having a pressure side wall and a suction side wallmeeting at a leading edge and a trailing edge of the airfoil, each ofthe pressure side wall and the suction side wall including raisedfeatures on an outer surface thereof, an interior of the spar includingcoolant cavities; a pressure side coversheet overlying the pressure sidewall, an inner surface of the pressure side coversheet being in contactwith the arrangement of raised features on the outer surface of thepressure side wall, thereby defining pressure side flow channels betweenthe pressure side wall and the pressure side coversheet; a suction sidecoversheet overlying the suction side wall, an inner surface of thesuction side coversheet being in contact with the arrangement of raisedfeatures on the outer surface of the suction side wall, thereby definingsuction side flow channels between the suction side wall and the suctionside coversheet, wherein the pressure side flow channels include apressure side cooling circuit, and/or wherein the suction side flowpathways include a suction side cooling circuit; delivering coolant froma first and/or a second of the coolant cavities into another of thecoolant cavities through the pressure side and/or the suction sidecooling circuit.

A fifteenth aspect relates to the method of the fourteenth aspect,wherein delivering the coolant through the pressure side and/or suctionside cooling circuit comprises directing the coolant toward the leadingedge of the airfoil.

A sixteenth aspect relates to the method of the fourteenth or thefifteenth aspect, wherein the first and/or the second of the coolantcavities comprises a trailing edge coolant cavity and/or a midspancoolant cavity, and wherein the other of the coolant cavities is aleading edge coolant cavity.

A seventeenth aspect relates to the method of any of the fourteenththrough the sixteenth aspects, wherein delivering the coolant throughthe pressure side and/or suction side cooling circuit comprisesdirecting the coolant toward the trailing edge of the airfoil.

An eighteenth aspect relates to the method of any of the fourteenththrough the seventeenth aspects, wherein the first and/or the second ofthe coolant cavities comprises a leading edge coolant cavity and/or amidspan coolant cavity, and wherein the other of the coolant cavities isa trailing edge coolant cavity.

A nineteenth aspect relates to the method of the eighteenth aspect,wherein the coolant is delivered from the leading edge coolant cavityinto the trailing edge coolant cavity through the pressure side coolingcircuit.

A twentieth aspect relates to the method of the nineteenth aspect,wherein the pressure side cooling circuit is in fluid communication withthe leading edge coolant cavity via inlet holes in the pressure sidewall, and in fluid communication with the trailing edge coolant cavityvia outlet holes in the pressure side wall.

A twenty-first aspect relates to the method of the twentieth aspect,wherein the pressure side wall includes additional inlet holes in fluidcommunication with the trailing edge coolant cavity; and furthercomprising delivering the coolant from the trailing edge coolant cavityinto a PS trailing edge cooling circuit.

A twenty-second aspect relates to the method of any of the eighteenththrough the twenty-first aspects, wherein the coolant is delivered fromthe midspan coolant cavity into the trailing edge coolant cavity throughthe suction side cooling circuit.

A twenty-third aspect relates to the method of the twenty-second aspect,wherein the suction side cooling circuit is in fluid communication withthe midspan coolant cavity via inlet holes in the suction side wall, andin fluid communication with the trailing edge coolant cavity via outletholes in the suction side wall.

A twenty-fourth aspect relates to the method of the twenty-third aspect,wherein the suction side wall includes additional inlet holes in fluidcommunication with the trailing edge coolant cavity; and furthercomprising delivering the coolant from the trailing edge coolant cavityinto a SS trailing edge cooling circuit.

In addition to the features mentioned in each of the independent aspectsenumerated above, some examples may show, alone or in combination, theoptional features mentioned in the dependent aspects and/or as disclosedin the description above and shown in the figures.

What is claimed is:
 1. A method of transferring coolant in a dual-wallairfoil, the method comprising: providing an airfoil comprising: a sparhaving a pressure side wall and a suction side wall meeting at a leadingedge and a trailing edge of the airfoil, each of the pressure side walland the suction side wall including raised features on an outer surfacethereof, an interior of the spar including coolant cavities; a pressureside coversheet overlying the pressure side wall, an inner surface ofthe pressure side coversheet being in contact with the arrangement ofraised features on the outer surface of the pressure side wall, therebydefining pressure side flow channels between the pressure side wall andthe pressure side coversheet; a suction side coversheet overlying thesuction side wall, an inner surface of the suction side coversheet beingin contact with the arrangement of raised features on the outer surfaceof the suction side wall, thereby defining suction side flow channelsbetween the suction side wall and the suction side coversheet, whereinthe pressure side flow channels include a pressure side cooling circuit,and/or wherein the suction side flow pathways include a suction sidecooling circuit; delivering coolant from a first and/or a second of thecoolant cavities into another of the coolant cavities through thepressure side and/or the suction side cooling circuit, the first and/orthe second of the coolant cavities comprising a leading edge coolantcavity and/or a midspan coolant cavity, and the other of the coolantcavities being a trailing edge coolant cavity, wherein the coolant isdelivered from the leading edge coolant cavity into the trailing edgecoolant cavity through the pressure side cooling circuit.
 2. The methodof claim 1, wherein delivering the coolant through the pressure sideand/or suction side cooling circuit comprises directing the coolanttoward the leading edge of the airfoil.
 3. The method of claim 1,wherein the first and/or the second of the coolant cavities comprises atrailing edge coolant cavity and/or a midspan coolant cavity, andwherein the other of the coolant cavities is a leading edge coolantcavity.
 4. The method of claim 1, wherein delivering the coolant throughthe pressure side and/or suction side cooling circuit comprisesdirecting the coolant toward the trailing edge of the airfoil.
 5. Themethod of claim 1, wherein the coolant is delivered from the midspancoolant cavity into the trailing edge coolant cavity through the suctionside cooling circuit.